In recent years, soft silicone hydrogel contact lenses, for example, Focus NIGHT & DAY™ and O2OPTIX™ (CIBA VISION), and PureVision™ (Bausch & Lomb) become more and more popular because of their high oxygen permeability and comfort. “Soft” contact lenses conform closely to the shape of the eye, so oxygen cannot easily circumvent the lens. Soft contact lenses must allow oxygen from the surrounding air (i.e., oxygen) to reach the cornea because the cornea does not receive oxygen from the blood supply like other tissue. If sufficient oxygen does not reach the cornea, corneal swelling occurs. Extended periods of oxygen deprivation cause the undesirable growth of blood vessels in the cornea. By having high oxygen permeability, a silicone hydrogel contact lens allows sufficient oxygen permeate through the lens to the cornea and to have minimal adverse effects on corneal health.
However, a silicone hydrogel material typically has a surface or at least some areas of its surface which is hydrophobic (non-wettable). Hydrophobic surface or surface areas will up take lipids or proteins from the ocular environment and may adhere to the eye. Thus, a silicone hydrogel contact lens will generally require a surface modification.
A known method for modifying the hydrophilicity of a relatively hydrophobic contact lens material is through the use of a plasma treatment, for example, commercial lenses such as Focus NIGHT & DAY™ and O2OPTIX™ (CIBA VISION), and PureVision™ (Bausch & Lomb). Advantages of a plasma coating is its durability, relatively high hydrophilicity (or good wettability), and low susceptibility to lipid and protein deposition and adsorption. But, plasma treatment of silicone hydrogel contact lenses may not be cost effective, because the preformed contact lenses must be dried before plasma treatment and because of relative high capital investment associated with plasma treatment equipments.
Another method for modifying the hydrophilicity of a relatively hydrophobic contact lens material is a layer-by-layer (LbL) polyionic material deposition technique (see for example, U.S. Pat. Nos. 6,451,871, 6,717,929, 6,793,973, 6,884,457, 6,896,926, 6,926,965, 6,940,580). This technique can provide a cost effective process for rendering a silicone hydrogel material wettable. However, such LbL coating may be less durable than a plasma coating for extended wear purpose.
Another method for modifying the surface hydrophilicity of a silicone hydrogel contact lens is the incorporation of wetting agents into a lens formulation for making the silicone hydrogel contact lens as proposed in U.S. Pat. Nos. 6,367,929 and 6,822,016. This method may be cost effective because after cast-molding of silicone hydrogel contact lenses there is no additional posterior process required for modifying the surface hydrophilicity of the lens. However, the wetting agents may not stay effective over time and may not provide a durable wettable surface. In addition, there may be hydrophobic surface spots which can be extremely susceptible to lipid/protein adsorption and deposition.
Therefore, there is a need for a method of producing silicone hydrogel contact lenses with wettable and durable coating (surface) in a cost effective manner.